As the dimensions of interconnect structures within a semiconductor device become increasingly smaller, there is a need for interlayer dielectric such as low dielectric constant films to, for example, reduce capacitance, power consumption, and cross noise. Low dielectric constant films, i.e., having a dielectric constant of 4.2 or less, are comprised of materials that include, but are not limited to, such as fluorine doped silicate glass (FSG), organosilicate glass (OSG), organofluoro-silicate glass (OFSG), polymeric materials such as silsesquioxanes (HSQ, HSiO1.5), methyl silsesquioxanes (MSQ, RSiO1.5 where R is a methyl group), and porous low dielectric constant materials.
In the manufacture of integrated circuits, surface planarity is a key processing step. To achieve the degree of planarity needed to produce ultra high density integrated circuits, chemical mechanical planarization is often employed. In CMP processes, polishing and removal of excess material is accomplished through a combination of chemical and mechanical means. In a typical CMP process, a wafer surface may be mechanically scrubbed via a polishing pad while chemically reactive slurry containing abrasive particles flows over and etches various surfaces of the substrate during processing. The combination of mechanical and chemical removal of material during polishing results in planarization of the surface.
One of the disadvantages of CMP may be a higher defect level observed on post-CMP cleaned substrates. The term “defects”, as used herein, relates to defects that may reduce the yield, or cause the loss, of the semiconductor device such as the particulates introduced onto the substrate resulting from processing such as submicron abrasive particles (e.g., SiO2 or Al2O3) from the CMP slurry; particulates either indigenous to or resulting from manufacturing processes such as the residue from the CMP process or reaction products of the CMP slurry; and water-mark type defects. It is necessary to remove the contamination prior to subsequent processing of the substrate to avoid degradation in device reliability and the introduction of defects.
One way to cleanse the substrate of CMP residuum is through one or more aqueous-based rinses in combination with some form of mechanical agitation to remove slurry chemical and abrasive residue from the surface of the substrate. U.S. Pat. No. 5,704,987 describes a two-step polishing method that uses a basic aqueous solution containing a nonionic polymeric surfactant and quaternary ammonium hydroxide in the first step and purified water in the second step. European Patent Application EP 1,065,708 describes a post-CMP cleaning method wherein the wafer is subjected to surfactant-containing megasonic baths that have a pH that matches the pH of the slurry to be removed. Published Application WO 00/14785 describes cleaning an organic dielectric surface after CMP treatment by a combination of mechanical or frictional agitation and aqueous alkaline solution containing a surfactant and a tetra alkyl quaternary ammonium hydroxide compound. Published Application WO 00/18523 describes a method for cleaning hydrophobic surfaces by applying a surfactant-containing solution may further include a chemical enhancer, optionally scrubbing, and then spin-rinsing the substrate.
Yet another method to cleanse the substrate surface of CMP residuum is to employ one or more post-CMP cleaning solutions. These solutions are typically tailored to react and remove certain types of residue such as etching residue (i.e., copper, aluminum, or other metal from the metallization layers) or CMP slurry residue (i.e., oxide or abrasive particles). U.S. Pat. No. 5,466,389 discloses an aqueous-based alkaline cleaning composition that contains a metal ion free base, a nonionic surfactant, and a buffering agent to maintain the pH of the composition between 8 and 10. U.S. Pat. No. 5,789,360 describes a post-CMP cleaning solution containing 0.1% to 99% phosphoric acid, 0.1% to 25% fluoroboric acid, and the balance deionized water. U.S. Pat. No. 6,194,366 discloses a post-CMP cleaning composition that contains a quaternary ammonium hydroxide, an organic amine, a corrosition inhibitor, and water.
Typical surfactants used in the post-CMP cleaning process tend to have poor dynamic wetting capability and high tendency to generate foam. Although they get easily absorbed onto substrate surface, they may be difficult to remove. Post-CMP cleaning is a very dynamic process requiring a surfactant with superior dynamic wetting ability. This is particularly important for hydrophobic surfaces such as low-k dielectrics.